1. Field of the Invention
The present invention relates to a processing system for manufacturing integrated circuits (ICs) and flat panel displays. More specifically, the invention relates to a susceptor and purge guide used to support a substrate in a processing system and prevent backside deposition on the substrate.
2. Background of the Related Art
Integrated circuits and flat panel displays are typically fabricated by depositing multiple layers of materials such as metals and dielectrics on a substrate and patterning the layers to form various structures. In the majority of applications, a single substrate such as a 100 mm, 200 mm or 300 mm substrate is used to form multiple die thereon. The trend has been to increase the size of the substrate while reducing the size of the devices so that more devices are formed on a single substrate. As a result, one important aspect of IC and flat panel display fabrication is to improve uniformity of deposited materials across the surface of the substrate and to reduce the overall edge exclusion which cannot be used to form viable die.
It is desirable to exclude deposited materials from the backside of the substrate, as well as from the edges of the substrate, to prevent the substrate from adhering to the susceptor on which it is supported during processing and to prevent material from depositing on areas of the substrate where the material may not adhere or be subject to flaking. Both backside deposition, as well as deposition on the edge of the substrate, may also result in particle formation in the system.
To combat the problems of backside deposition and edge deposition, purge gases delivered from the backside of the substrate and purge guides or rings have been used. One such purge guide is described in U.S. Pat. No. 5,516,367, entitled "Chemical Vapor Deposition Chamber with a Purge Guide", by Lei et al., which is incorporated herein by reference. FIG. 1 is a cross sectional view of a prior art substrate support member 10 and purge guide 12. The purge guide is supported on a shoulder 14 formed on the substrate support member and includes an inner lip 16 which overhangs or contacts the edge of a substrate 18. The inner lip 16 may define a narrow passage between its lower surface and the substrate through which a purge gas is flowed. The purge gas is delivered through the support member to the edge of the substrate having the purge guide supported above the substrate. However, gas flow outwardly through the gap between the purge guide 12 and shoulder 14 of the substrate support member creates a low pressure region which draws the reaction gases to the edge and backside of the substrate and result in unwanted deposition thereon.
One problem encountered with the available purge guides is that the flow rate of the backside gases must be tightly controlled to prevent edge and backside deposition while facilitating deposition uniformity on the substrate surface. The flow rate of purge gas delivered between the purge guide and the substrate must be controlled to prevent adverse effects on deposition uniformity towards the outer edge of the substrate due to the purge gas disrupting process gas flow over the substrate surface.
Another problem encountered is that the requirements of edge exclusion have become more demanding. In the past, it was acceptable for the exclusion area on the perimeter of the substrate to extend up to 6 mm from the substrate edge with ninety percent (90%) film thickness at 6 mm inward from the edge. More recently, the demand has been increased to only 3 mm of exclusion with ninety to ninety-five percent (90-95%) film thickness at 3 mm inward from the edge. Accordingly, the purge guides and purge flow must be adapted to accomplish these increased demands.
Therefore, there is a need for a purge guide and susceptor to support a substrate during processing and to prevent backside and edge deposition with a narrow exclusion width around the perimeter of the substrate.